China's multiple world and Olympic badminton champion Lin Dan cleared up any doubts about his master's degree, saying his thesis was on badminton.

"The questions about my master's degree were fair, since I was always training or playing in competitions, leaving little time for studying," Lin said at the launch ceremony for the Ling Foundation in Nanjing, Jiangsu province, on Saturday.

"But the teachers are very good in my school, and my thesis for the degree is also on the strategy of badminton on the world stage. I have been playing badminton for 12 years, so I think I have the right to address this topic," he said.

The 29-year-old received his Master of Public Administration from Huaqiao University in Quanzhou, Fujian province, last Wednesday, raising doubts from the public that he'd managed to earn the degree in the midst of his tough training schedule

In 2006, the Bayi Badminton club reached a cooperation agreement with the university, under which the club sent coaches to the university in return for study opportunities for its players.

Since the London Olympics, Lin hasn't taken part in any international competitions. He held a wedding ceremony with former women's world No 1 Xie Xingfang last month.

Launching the Ling Foundation, which was set up by TaiLG brand of Shenzhen Shenling car company to support grassroots sports in China and other public welfare activities, was Lin's latest social affair.

"Attending public welfare activities will be an important part of my future career," said Lin, who collected 253,000 yuan ($40,450) for the foundation by selling TaiLG electric bikes with his autograph, badminton crackers and bags at the ceremony.

"I hope I can visit some schools and students with the foundation next year to promote badminton among youngsters there," he said.